1. Field of the Invention
The present invention relates generally to the field of laundry and other article-drying equipment and, more particularly, to an improved combustion chamber used to advantageously provide large volumes of very hot air to high-production commercial dryers.
2. Description of the Prior Art
An overall view of typical prior art in industrial laundry dryer-conditioners, generally referred to in the industry as merely "dryers", may be found by referring to U.S. Pat. Nos. 2,604,313, 2,643,463, 3,443,323, 3,861,865 and 4,015,930. Dryers such as those discussed in these patents and, for that matter, industrial dryers in general, require large volumes of air having a temperature, in the tumbler of the dryer, in the range of 300.degree. to 350.degree. F., which elevated temperature air flow combines with the tumbling action of the dryer to achieve rapid, yet safe, drying.
The high temperature of the air flowing through the dryer is achieved by the burning of fuel such as natural gas, propane, butane, or fuel oil in a combustion chamber from which hot air is supplied to the dryer housing, generally with the aid of an air pump or blower. The fuel is mixed with appropriate portions of air to obtain clean burning of the fuel, and is introduced into the combustion chamber under pressure. Internal temperatures in the combustion chamber may typically range from 400.degree. to 700.degree. F., and it may therefore be apprecited that the high temperature of operation is a factor in the design of the combustion chamber.
The present state-of-the-art of the combustion chamber is illustrated in U.S. Pat. No. 3,861,865, and utilizes double wall construction with between-wall cooling by intake (make-up) air as well as an air barrier to eliminate the need for a refractory endpiece. While this design offers significant advantages over previous such combustion chambers, it has, as do other previous designs, several disadvantages which are discussed at length below. The solution to these disadvantages in a combustion chamber offering at least as economic and dependable operation as presently existing devices will present to its manufacturer a significant competitive advantage in the industry.
The first of these problems is related to the placement of the burner in the front wall of the combustion chamber. At best it is inconvenient to have the burner in the front of the dryer, since the fuel line must be routed around to the front of the machine. Since the portion of exhaust from the dryer which is to be recirculated back into the dryer with the hot air flow in present devices enters the combustion chamber at the end opposite the burner, it is apparent that the flow of hot gas generated by the burner will move in a direction opposite to the flow of exhaust gas which is being recirculated. This counterflow problem results in a loss in efficiency due to swirl occurring in the combustion chamber, as well as making the regulation of the amount of exhaust gas recirculated relatively difficult to control.
A closely related problem is caused by the differing locations at which fresh air is supplied to the dryer and exhaust air is purged from the dryer. In the arrangement shown in U.S. Pat. No. 3,861,865, fresh air enters the combustion chamber from both ends of the dryer, and exhaust air leaves through an exhaust stack at the back of the dryer. It has been found desirable to have a more hermetically sealed combustion chamber, where both fresh air and exhaust air flows are supplied through ducting at the same end of the chamber. This simplifies the construction of the chamber and permits better control of the air flow.
In addition, the preferred method of supplying fresh air and removing exhaust air is to use a coaxial tube arrangement, with the fresh air being ducted in a tube contained within the stack carrying out the exhaust air. This technique offers the advantage fo preheating the fresh air without expending any further energy, thereby reducing the amount of fuel which must be burned to heat the fresh air prior to supplying it to the dryer. This type of ducting arrangement is difficult to use with a combustion chamber having the air intake on one end of the combustion chamber and the exhaust on the other end, and bulky and expensive manifolds and added ducting work only with diminished efficiency. It is therefore apparent that it is highly desirable to have the fresh air intake as close to the exhaust as possible, and it is further desirable to have the system hermetically sealed.
A further problem in existing combustion chambers for dryers relates to the problems of temperature control and air mixture. Clothing in the dryer can tolerate a fairly high temperature when wet, in the neighborhood of 300.degree.-350.degree. F., as stated above. However, when the clothes are about 25% through the drying cycle, although still damp, they can no longer tolerate higher temperatures without scorching. Accordingly, the temperature should be reduced at this point in the drying cycle. One way to do this is by reducing the level of the burner. It is desirable to effect this reduction in temperature by the introduction of a greater amount of cooler fresh air, rather than to lower the temperature exclusively by lowering the level of the burner.
It may therefore be seen that a number of areas for improvement exist with respect to combustion chambers for dryers. It is of course also apparent that while the combustion chamber should be as inexpensive to purchase as possible, the efficiency of operation is most important, since even small gains in efficiency translate over a long period into relatively large savings. Finally, it is desirable that an improved combustion chamber may be retrofitted onto older dryers so the operators of such dryers may also obtain the attendant advantages of the improved combustion chamber.